What is the way forward for the retro community to run a modern Wayland system on older hardware?
Hopefully someone more knowledgeable can chime in or correct me
The reason is that Mesa includes "software rendering" drivers for both OpenGL ("llvmpipe") and Vulkan ("lavapipe"). As the name(s) might suggest, they use LLVM to JIT shaders for your CPU (supporting SIMD up to AVX2, last I checked - although typical compositing shaders tend to get pattern-matched and replaced with plain `memcpy`s etc.).
So you should always be able to run a fully-featured Wayland desktop (albeit limited in performance by your CPU), on any unaccelerated framebuffer, nowadays (and I remember doing this even before Plasma 6 launched, it may be older than usable Wayland desktops tbh - the Mesa code sure is, but maybe distros hadn't always built those drivers?).
I'm curious why that's something that should happen. Shouldn't the 'retro community' be happy with retro software and not expect cutting edge software to work on their hardware?
That being said, your bigger problem is trying to view modern websites on 1080p displays on that ancient hardware...